This invention relates generally to robot devices, and, more particularly, to apparatus for positioning a movable part of a robot in relation to a surface.
Robots are mechanical devices which can perform tasks in a manner that simulates human activity. One type of robot, the industrial robot, is finding widespread acceptance in manufacturing and other industrial operations, and promises many benefits in the automation of repetitive industrial operations. A typical industrial robot includes a stationary portion, usually referred to as the body, and a movable portion, usually referred to as the arm, wrist or hand, with the movable portion adapted for performing an operation on a workpiece. By way of example, robot arms can assemble components, join components as by welding, and finish components as by cleaning and painting.
In most industrial operations, a critical aspect of the operation of robot devices is the precise positioning of the movable robot arm with respect to the workpiece. In the simplest robots, each workpiece must be positioned at an exact location and orientation with respect to the robot arm, so that no separate sensing device is necessary to orient the robot arm with respect to each successive workpiece. For the robot arm to perform operations which require it to move over the surface of a workpiece, usually referred to as a continuous path operation, as in the painting of a part, a coordinate map of the surface of the workpiece must be coded into the memory of a computer which controls the trajectory of the moving robot. In such simple robots, failure to orient a workpiece in its exactly proper position can result in a failure of the operation to be performed by the robot. Further, such robots must be dedicated in the sense that a large amount of information concerning each particular type of workpiece must be coded into the control computer, and changes in the workpiece require reprogramming.
A more complex type of control utilizes some form of sensor to gather information about the workpiece and transmit this information to the robot, thereby providing a control input to the robot. As an example, a tactile or proximity sensor incorporated in the hand of the robot may be used to indicate the presence of a workpiece, and may also give some basic information about its orientation. Multiple tactile sensors can also be used to advantage. In a somewhat similar approach, light sources and photo cells may be used in combination to provide light beams which are broken when a workpiece is moved into position. However, both these approaches have not proved sufficiently versatile for use in many applications, especially where the robot arm is not in contact with, or in the close proximity of, the workpiece.
More recently, solid state video imaging systems have been developed for controlling robot devices. Such video imaging systems typically operate in a manner similar to television, wherein a visual field is scanned by a solid state camera to produce a sequential electronic signal having the visual image encoded thereupon. The digital signal is used to reconstruct an image on a television viewer or, for the purposes of controlling a robot, may be analyzed by existing pattern recognition techniques to provide information to the robot about the position, shape, and orientation of the workpiece, and the spacing of the robot arm from the workpiece. While robots having electronic video imaging systems represent an advance over the more primitive robots, such systems have severe disadvantages that limit their utilization in many applications. In many adverse working environments it is impossible to provide enough light to the camera. Image enhancement techniques are known, but in adverse environments the image may be insufficient for their use. More significantly, however, in all working environments such video imaging systems require a complex system utilizing extensive hardware components, including solid state cameras, a monitor and a computer, and complex programming and algorithms to recognize the patterns. The information from such video imaging systems is provided to a controlling computer which follows the encoded coordinate maps to guide the robot to take each successive step. Once the robot moves to its next step, the entire process of detecting the robot position and guiding it further must be repeated. In addition, the information transmission between interfaced devices is inherently slow, so that the system can communicate at a rate no greater than about 10-50 functions per second, thus limiting the speed and performance of the robot.
Robots equipped with video imaging systems must be controlled and their movement integrated by a central controller computer. This computer must necessarily be large and complex to provide the robot controller with a high degree of versatility, since it is often necessary to perform major computer reprogramming if the design of the workpiece is changed. For example, the computer may be programmed with a mathematical model of the surface of the workpiece for use in the pattern recognition function, and this mathematical model must be changed when the robot is to operate upon a different or modified workpiece. To some extent, such computers are therefore dedicated to use with a single type of workpiece, although the dedication may be changed by reprogramming.
There has been a need for a more versatile, non-dedicated apparatus to enable robots to sense the positioning of their movable arms with respect to the surface of a workpiece. Desirably, such an apparatus would be operable in adverse environments and would permit more rapid signal processing with less complex, less costly hardware and software. Such apparatus should be operable to allow the movable part of the robot to be positioned in a controllable manner adjacent the workpiece, with little or no preprogramming required for adapting the robot to operation in a continuous path on different workpieces. The present invention fulfills this need, and further provides related advantages.